Galactose is a monosaccharide, which is mostly found in the milk sugar or lactose, where galactose is bound to glucose. In some sour milk products, lactose has been decomposed into glucose and galactose.
Galactose has many applications in the pharmaceutical field and in food technology. In the pharmaceutical field, galactose is useful for example as a pharmaceutical intermediate for several medicines. Furthermore, galactose is also useful as a stabilizer in intravenous solutions for medical use. In food technology, galactose has been found useful for example as a potential energy source in sports drinks. Galactose is also useful in cell culture media as a nutrient or as an inducer in the fermentation.
Galactose is as a rule obtained by hydrolyzing lactose (a disaccharide consisting of glucose and galactose), which is found in dairy products, such as milk. Recently, for example due to the BSE disease, there is an increased interest to produce galactose of non-dairy and non-animal origin.
British Patent 925 380, Joseph Donelly (published May 8, 1963) discloses a process based on crystallization for purifying crude anhydrous (D)(+)-galactose, which has been produced by the degradation of an oligosaccharide, such as lactose, melibiose and raffinose. The purification process comprises dissolving the crude galactose in methyl alcohol or ethyl alcohol or a mixture thereof with water, removing the undissolved impurities and recovering galactose from the solution by crystallization, optionally followed by recrystallization. The purity of the galactose product has not been reported.
WO 99/53088, Deva Processing Services Ltd (published 21 Oct. 1999) discloses a process for the production of galactose from galactose-containing disaccharide or polysaccharide, such as lactose, by hydrolysis and enzymatic treatment. The galactose obtained by this process is not crystallized. It is recited in the reference that it is extremely difficult to separate contaminants from galactose so that galactose with a pharmaceutical grade purity would be obtained.
Galactose is rather rare in plant-based materials, but it has been found in not very abundant amounts in various plants as a multicomponent mixture with other sugars and carbohydrates. Galactose has been found for instance in wood resources, where galactose is, present as an admixture with other carbohydrates and lignin components. Softwood hemicelluloses are especially rich in galactose. Galactose has also been found in various natural gums and pectin-based materials.
Wood resources, for example, may thus be potential sources for the recovery of plant-based galactose. Spent liquors obtained from acid wood-pulping processes, especially liquors from softwood pulping processes can be mentioned as examples of potential starting materials for the recovery of galactose.
It is known in the state of the art to recover galactose from various plant-based raw materials using methods selected for example from extraction, hydrolysis and treatment with adsorbents and cation and anion exchangers, followed by crystallization. Chromatographic methods for the recovery of galactose-containing solutions from plant-based materials are also known in the state of the art. However, these chromatographic methods for the recovery of galactose-containing solutions generally provide galactose as a mixture with other closely-related sugars. Galactose has not been recovered from said sugar mixtures.
EP 1 046 719 A1, Cargill B. V. (published 25 Oct. 2000) recites that rare sugars, for example arabinose, rhamnose, fucose and mannose are unwanted in galactose preparations, because the presence of these components will limit for example the scope of food applications in which the galactose preparations may be used. The EP publication discloses a process based on hydrolysis for manufacturing D-galactose from an oligosaccharide-containing legume composition which contains D-galactose mainly in chemical combination with D-glucose and/or D-fructose. The oligo-saccharide-containing material is typically derived from soybeans, rapeseeds or sunflower seeds or mixtures thereof. In the examples, a galactose preparation containing D-galactose in an amount of 3 to 10% on a dry weight basis was recovered. In accordance with Example 4 of the reference, the D-galactose content of the preparation may be increased by chromatography. The galactose preparation obtained by the process is not crystallized.
U.S. Pat. No. 6,451,123 B1, Saska, M., Board of Supervisors of Louisiana State University of Agricultural and Mechanical College (published 17 Sep. 2002) discloses a method of separating a carbohydrate selected from xylose, mannose, galactose, arabinose, glucose, xylitol, arabitol, galactitol and mannitol from an aqueous phase comprising said carbohydrate and at least one other non-identical component (a sugar or a sugar alcohol). The aqueous phase from which the carbohydrates are separated may be a soft-wood liquor, a hardwood liquor or a hydrolysate thereof, for example. It is recited that the separation is carried out using a strong base anion exchange resin in an anion form, which is other than hydroxyl form. The resin used for the separation is conditioned with a sufficient concentration of hydroxyl ion. In a typical application of the method, a resin in a chloride form is used. In this process, galactose is not recovered.
U.S. Pat. No. 6,451,123 B1 mentioned above refers to man-nose/galactose separation with a strong acid cation selected from Ca2+ and Pb2+ (page 2, Table II, lines 65 and 66) disclosed by Caruel H. et al.
Caruel, H. et. al. have studied carbohydrate separation in “Carbohydrate separation by ligand-exhange liquid chromatography: correlation between the formation of sugar-cation complexes and the elution order”, J. Chromatography 558(1), pp. 89-104 (1991). It is recited that carbohydrate separation (hexoses, pentoses and corresponding polyols) was studied by liquid chromatography using ligand exchange on a strong acid cation-exchange resin column with water as the eluent. Seven cations (Ca2+, Sr2+, Ba2+, Pb2+, Y3+, La3+ and Pr3+) were tested.
U.S. Pat. No. 3,471,329, Laevosan-Gesellschaft Chem. Pharm Industrie Frank & Dr. Freudl (published Oct. 7, 1969) discloses a process for the separation of different sugars from a mixture thereof, comprising reacting a cation exchange resin with hydrazine, and then contacting an aqueous-alcoholic solution of said mixture of sugars with the hydrazine-containing cation exchange resin, followed by washing the sugar-containing resin to fractionate the sugars and obtain the individual sugars present in said sugar mixture in the different fractions. The cation exchange resin may contain highly acid active groups, such as sulphate, carboxyl or phosphite groups. The separation of fructose and galactose is disclosed in Example 3 of said reference. It is also recited in Example 3 that the galactose fractions gave pure crystallized galactose after crystallization. However, the feed solution is not a hemicellulose hydrolysate.
U.S. Pat. No. 5,084,104, Cultor Ltd, Heikkilä et al. (published Jan. 28, 1992) discloses a process for the production of a high purity xylose fraction from a xylose-rich solution further containing other monosaccharides, using chromatographic fractionation with a strong base anion exchange resin in sulphate form. Galactose is not recovered in this process.
U.S. Pat. No. 4,772,334, Kureha Kagaku Kogyo Kabushiki Kaisha (published Sep. 20, 1988) discloses a process for producing highly pure rhamnose from gum arabic by hydrolyzing gum arabic with a mineral acid to form a liquid hydrolysate comprising L-rhamnose, L-arabinose and D-galactose and subjecting the neutralized and clarified hydrolysate to strongly cationic ion-exchange chromatography to separate D-galactose and L-arabinose from L-rhamnose using a mixture of water and organic solvent as an eluant. In the examples, a Na+ form resin is used. Galactose is not recovered.
U.S. Pat. No. 4,857,642, UOP (published 15 Aug. 1989) discloses a process for separating arabinose from an aqueous feed mixture containing arabinose and at least one other monosaccharide from the group consisting of aldoses and ketoses by contacting the feed mixture with an X-zeolite adsorbent containing ammonium cations. Said other monosaccharide is typically selected from glucose, xylose, galactose and mannose. It is recited that arabinose is selectively absorbed by the X-zeolite adsorbent. Galactose is not re-covered.
Bollini, M & Galli, R (“Separation and determination of the sugars of bisulfite liquors”, Stn. Sper. Cellul., Carta Fibre Tess. Veg. Artif., Milan, Italy. Ind. Carta (1975), 13(10), 392-4) have identified and determined mannose, glucose, galactose, arabinose, xylose, hexoses and pentoses in a bisulfite liquor after the separation of lignosulphonates. The liquor was treated with EtOH, the precipitate centrifuged, lignosulphonates separated, purified with cation and anion exchange resins and subjected to gas chromatographic and colori-metric determinations.
Sinner, M., Simatupang, M. H. & Dietrichs, H. H. (“Automated Quantitative Analysis of Wood Carbohydrates by Borate Complex Ion Exchange Chromatography”, Wood Science and Technology, 1975, pp. 307 to 322) describe a simple automated analytical method for the separation and quantitative determination of sugars from acidic and enzymatic hydrolysates of wood polysaccharides via borate complex ion exchange chromatography. The sugars separated in this way may include mannose, fructose, arabinose, galactose, xylose, glucose and disaccharides like xylobiose, cellobiose and sucrose.
Guihard, L., Dendene, K. & Bariou, B. (“Sugar separation by low pressure chromatography”, Lab. GPSA, ENSCR, Rennes Beaulieu, Fr. Recents Progrés en Genie des Procédés (1991), 5 (15, Procédés Sep.), 167-72 disclose the separation of lactose from other milk sugars using AG 50W-X8 cation exchanger. A syrup containing galactose, lactose and lactulose was first eluted on the resin in Na+ form, eliminating the galactose fraction. The product containing lactose and lactulose was then eluted on the resin in Ca2+ form giving lactulose in practically pure form. Galactose is not recovered in this process.
Indian Patent IN 158940 A, Council of Scientific and Industrial Research (India), (published 21 Feb. 1987) discloses a process for the preparation of pure D-galactose from green Aegle marmelos fruit-gum. In this process, said fruit material is subjected to two-step hydrolysis with H2SO4, followed by deionization treatment with Amberlite IR 120 (H+) and IR-4B (OH−). The product thus obtained is purified with activated carbon, and the solution is heated to a temperature of less than 40° C. under reduced pressure to give a syrup. The syrup is treated with 100 ml hot MeOH and 8-10 ml water, to crystallize D-galactose.
Ingle, T. R, Kulkarni, V. R, Vaidya. S. H. & Pai, M. U., Natl. Chem. Lab, Poona, India, Res. Ind. (1976), 21(4), 243-6 disclose a commercial process for the preparation of D-galactose from cashew nut shells. In this process, the cashew nutshell material is subjected to aqueous extraction, hydrolysis with H2SO4, concentration to a syrup, extraction, decolorization with activated charcoal, concentration and crystallization, followed by drying and powdering of the crystalline D-galactose.
Serdyuk, L. V, Dudkin, M. S., Gerzhov, A. F., Odess. Tekhnol. Inst. Pishch. Prom. im. Lomonosova, Odessa, USSR, Izv. Vyssh. Ucheb. Zaved. Pishch. Tekhnol. (1974), (2), 28-30 disclose potato as raw material for the production of concentrated solutions of simple sugars, including galactose. It is recited that the hydrolysis of potato material with 3% H2SO4 at 98 to 100° C. for 3.5 to 4 hours yielded a concentrate containing glucose, galactose and arabinose.
Kato, Y. et al. disclose an affinity chromatographic adsorbent for carbohydrate separation in Japanese Patent JP 06201671, Cosmo Sogo Kenkyusho Kk, Cosmo Oil Co Ltd, (published 22 Jul. 1994). It is recited that the affinity chromatographic adsorbent is a porous crosslinked copolymer containing alcoholic hydroxyl groups and lectin. It is also recited that the adsorbent is used in HPLC for the separation of carbohydrates, especially mannose and galactose.
Yamane, T. et al. disclose decomposition of raffinose by an enzymatic reaction applied in a factory-process in Japanese beet sugar factories in Sucr. Belge/Sugar Ind. Abstr. (1971), 90(7), 345-348. It is recited that raffinose is decomposed by α-galactosidase into sucrose and galactose.
Dugal. H. et al. disclose enzymatic modification of locust bean and guar gums in IPPTA (1974), 11(1), 29-35. The effect of time, pH, temperature and enzyme and substrate concentration on the hydrolysis of locust bean gum and guar by α-galactosidase isolated from sprouted guar seeds was studied and the hydrolyzed gums were characterized by X-ray diffraction and molecular weight determination. It is recited that the enzymatic hydrolysis of gums liberated galactose, arabinose and mannose. However, there is no xylose present in the substances used for the separation.
Non-published Finnish Patent Application 20012605, Danisco Sweeteners Oy discloses a method of recovering mannose from a solution derived from biomass by subjecting said solution to a chromatographic separation process using at least one chromatographic separation resin which is at least partly in Ba2+ form and at least one chromatographic separation resin which is in other than Ba2+ form. The latter resin is a cation exchange resin, where the cation is preferably Ca2+. The starting biomass-derived solution typically contains mannose in admixture with other sugars, such as xylose, galactose, glucose, rhamnose, arabinose and fructose. Galactose is not recovered.
It appears from the above description of the prior art that it is known to prepare galactose-containing solutions from raw materials based on hemicellulose. However, it has been found difficult to produce pure crystalline D-galactose, because it is especially cumbersome to separate galactose from other sugars, especially from mannose and xylose, but also from arabinose and rhamnose, when the content of galactose in the starting solution is low.
This problem has now been solved in accordance with the present invention by providing a combination of chromatographic fractionation and crystallization to obtain pure crystalline galactose from plant-based hemicellulsose raw materials.